1. Field of the Invention
The present invention relates to a color selective electrode of a cathode ray tube, and more particularly to an aperture grill for such a tube.
In a color selective electrode, for example, an aperture grill of a cathode ray tube of the invention, where a damper wire is stretched on grid elements by means of spring elements secured on both support members of the color selective electrode, each spring element is provided with a locking member which can temporarily fix the damper wire by shifting it from a prescribed position, so that during the forming of a fluorescent surface, the damper wire is temporarily fixed to the locking member while a carbon stripe, a fluorescent stripe or the like is formed, and after forming the fluorescent surface the damper wire is restored to the prescribed non-locked position, whereby deterioration of the picture quality due to so-called damper shadow, can be suppressed.
2. Description of the Prior Art
As shown in FIG. 1, in a cathode ray tube of, for example, Trinitron (registered Trademark) configuration, an aperture grill 1 is used as color selective electrode. The aperture grill 1 comprises a frame 13 composed of a pair of arms 2 and a pair of support members 5, and a number of linear grid elements 3 stretched between the arms 2 at prescribed pitches. A damper wire 4 is stretched on the surface of the grid elements 3 of the aperture grill 1 so that the grid elements 3 are prevented from deviation and deterioration of the color quality due to resonance by external vibration is minimized. The damper wire 4 is a thin wire made of tungsten or the like and attached to spring elements 6 by a thin strip 7 of stainless steel by means of seam welding. The support ends of elements 6 are similarly fixed to the support members 5 of the aperture grill 1 by welding.
As above described, in the cathode ray tube using the aperture grill 1 with the damper wire 4 stretched thereon, deterioration of the picture quality based on so-called damper shadow may occur. Damper shadow is produced in the following manner. In the process of forming a fluorescent surface as shown in FIG. 6A, when exposure is performed with ultraviolet ray 7 and carbon stripes and fluorescent stripes 8 are formed, a, shadow region 9 due to the damper wire 4 produces a defect portion or thinned portion 10 in the carbon stripes or the fluorescent stripes 8. After completing the fluorescent surface, when an image is reproduced with an electron beam 11 as shown in FIG. 6B, the thinned portion 10 is overlaid with the shadow region 9 produced by the damper wire 4 interrupting the electron beam so that the fluorescent stripes 8 in the thinned portion 10 are not lit. Consequently, the damper shadow is produced.
This problem of damper shadow becomes significant as the cathode ray tube becomes of high precision. In order to solve the problem of damper shadow, a method of attaching a damper wire 4 as shown in FIG. 7 has been proposed. In this method, the damper wire 4 is attached to a certain position of a grid element 3 and a fluorescent surface is formed as shown in FIG. 7A. Next, the damper wire 4 is shifted a suitable distance from the original position whefeby the position of the damper wire 4 at the final state is determined as shown :n FIG. 7b. In this arrangement, the problem of damper shadow caused by the double factors, (the shadow 9 of the damper wire 4 during forming the fluoresent surface and the shadow 9 of the damper wire 4 during the image reproduction,) as in the prior art (refer to FIGS. 1, 6A and 6B), is reduced to one-half.
In order to change the attaching position of the damper wire 4 before forming the fluorescent surface and after forming it, in the prior art, the spring material 6 and the damper wire 4 are attached individually to different respective positions. Although the problem of damper shadow can be reduced in this construction, excessive labor for the temporary fixing is required and the troublesome work to change the attaching positions is required.